U.S. patent application number 14/123707 was filed with the patent office on 2014-06-05 for method and systems for semiconductor chip pick & transfer and bonding.
This patent application is currently assigned to ORION SYSTEMS INTEGRATION PTE LTD. The applicant listed for this patent is Amlan Sen. Invention is credited to Amlan Sen.
Application Number | 20140154037 14/123707 |
Document ID | / |
Family ID | 47259627 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140154037 |
Kind Code |
A1 |
Sen; Amlan |
June 5, 2014 |
METHOD AND SYSTEMS FOR SEMICONDUCTOR CHIP PICK & TRANSFER AND
BONDING
Abstract
Various embodiments provide a system for pick and transfer of
semiconductor chips. The system comprises: a rotating arm; two pick
up heads attached at respective end portions of the rotating arm;
and a camera system for inspecting a chip pick-up position in a
vertical line of sight configuration. Also, an axis of rotation of
the rotating arm is offset from the line of sight. Various
embodiments also provide a corresponding method.
Inventors: |
Sen; Amlan; (Singapore,
SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sen; Amlan |
Singapore |
|
SG |
|
|
Assignee: |
ORION SYSTEMS INTEGRATION PTE
LTD
Singapore
SG
|
Family ID: |
47259627 |
Appl. No.: |
14/123707 |
Filed: |
May 31, 2012 |
PCT Filed: |
May 31, 2012 |
PCT NO: |
PCT/SG2012/000190 |
371 Date: |
February 18, 2014 |
Current U.S.
Class: |
414/744.2 ;
414/800 |
Current CPC
Class: |
H01L 2224/75651
20130101; H01L 2924/01075 20130101; H01L 2924/014 20130101; H01L
2924/01005 20130101; H01L 2924/01029 20130101; H01L 21/67144
20130101; H01L 24/75 20130101; H01L 2924/01006 20130101; H01L
2224/75822 20130101; H01L 2224/7525 20130101; H01L 21/68707
20130101; H01L 2224/75702 20130101; H01L 2224/75753 20130101 |
Class at
Publication: |
414/744.2 ;
414/800 |
International
Class: |
H01L 21/687 20060101
H01L021/687 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2011 |
US |
61492824 |
Claims
1. A system for pick and transfer of semiconductor chips
comprising: a rotating arm; two pick up heads attached at
respective end portions of the rotating arm; and a camera system
for inspecting a chip pick-up position in a vertical line of sight
configuration; wherein an axis of rotation of the rotating arm is
offset from the line of sight.
2. The system as claimed in claim 1, wherein the pick up heads are
angled relative to a longitudinal axis of the rotating arm.
3. The system as claimed in claim 1, wherein the pick up heads are
moveably attached to the rotating arm.
4. The system as claimed in claim 3, further comprising means for
retracting the pick up heads during rotation of the pick up heads
away from the chip pick-up position.
5. The system as claimed in claim 4, wherein the means for
retracting comprises a cam for guiding the pick up heads during
rotation of the rotating arm.
6. The system as claimed in claim 1, wherein the camera system
comprises a substantially horizontal camera and a reflecting
element for achieving the vertical line of sight configuration
7. A method for pick and transfer of semiconductor chips, the
method comprising: providing a rotating arm; providing two pick up
heads attached at respective end portions of the rotating arm;
providing a camera system for inspecting a chip pick-up position in
a vertical line of sight configuration; and rotating the rotating
arm for pick and transfer of the semiconductor chips, wherein an
axis of rotation of the rotating arm is offset from the line of
sight.
8.-56. (canceled)
Description
FIELD OF INVENTION
[0001] The present invention relates broadly to method and systems
for Semiconductor Chip Pick & Transfer and Bonding
BACKGROUND
[0002] Method and systems for Semiconductor Chip Pick &
Transfer and Bonding are widely used in the semiconductor
industries, in particular in semiconductor fabs or foundries.
Ongoing efforts are being made to improve various aspects of such
methods and systems, including with a view to improving throughput,
accuracy, reliability, and/or cost associated with the methods and
systems.
[0003] Furthermore, efforts are also being made with a view to
improving the resulting devices, in particular the chip/substrate
entity, including the reliability, durability, dimensioning, and/or
electrical properties of solder bonds between the chip and the
substrate.
[0004] Embodiments seek to provide method and systems for
Semiconductor Chip Pick & Transfer and Bonding that seek to
address one or more of the above improvement efforts.
SUMMARY
[0005] Various embodiments provide a system for pick and transfer
of semiconductor chips comprising: a rotating arm; two pick up
heads attached at respective end portions of the rotating arm; and
a camera system for inspecting a chip pick-up position in a
vertical line of sight configuration; wherein an axis of rotation
of the rotating arm is offset from the line of sight.
[0006] In an embodiment, the pick up heads are angled relative to a
longitudinal axis of the rotating arm.
[0007] In an embodiment, the pick up heads are moveably attached to
the rotating arms.
[0008] In an embodiment, the system further comprises means for
retracting the pick up heads during rotation of the pick up heads
away from the chip pick-up position.
[0009] In an embodiment, the means for retracting comprises a cam
for guiding the pick up heads during rotation of the rotating
arm.
[0010] In an embodiment, the camera system comprises a
substantially horizontal camera and a reflecting element for
achieving the vertical line of sight configuration
[0011] Various embodiments provide a method for pick and transfer
of semiconductor chips, the method comprising the steps of:
providing a rotating arm; providing two pick up heads attached at
respective end portions of the rotating arm; providing a camera
system for inspecting a chip pick-up position in a vertical line of
sight configuration; and rotating the rotating arm for pick and
transfer of the semiconductor chips, wherein an axis of rotation of
the rotating arm is offset from the line of sight.
[0012] Various embodiments provide a device for bonding a
semiconductor chip onto a substrate comprising: a pick-up tip for
the semiconductor chip; a heater for heating the pick-up tip for
heating of the chip prior to bonding; and means for directing a
gaseous cooling stream towards the pick-up tip.
[0013] In an embodiment, the pick-up tip is attached on a mounting
block, and the heater is disposed in the mounting block.
[0014] In an embodiment, the means for directing the cooling stream
comprises a conduit element mounted to the mounting block.
[0015] In an embodiment, the conduit element is mounted to the
mounting block via a thermally insulating element.
[0016] In an embodiment, the conduit element is configured to
direct the cooling stream from three sides of the mounting
block.
[0017] In an embodiment, the conduit element is configured to
receive the cooling stream in a downward direction along one side
of the mounting block, and comprises a diverting portion for
diverting the cooling stream substantially horizontally towards the
pick-up tip mounted at a bottom of the mounting block.
[0018] In an embodiment, the diverting portion comprises a ledge
extending inwardly towards the pick-up tip.
[0019] Various embodiments provide a method of forming a solder
joint between a semiconductor chip and a substrate, the method
comprising the steps of: melting a solder disposed between the chip
and the substrate, the chip and the substrate being separated by a
first distance; retracting the chip from the substrate while the
solder is in a molten state such that the chip and the substrate
are separated by a second distance; and solidifying the solder
while the chip and substrate are separated by the second
distance.
[0020] In an embodiment, the solder is disposed on the chip and
melted prior to contact with the substrate.
[0021] In an embodiment, the semiconductor chip is preheated to a
first temperature lower than the melting temperature of the solder
disposed on the chip.
[0022] In an embodiment, the solidifying of the solder comprises
directing a cooling stream towards the solder.
[0023] In an embodiment, the cooling stream is directed towards the
solder while a chip and/or substrate heater continue to provide
heat to the chip and/or substrate.
[0024] In an embodiment, the second distance is chosen such that
the formed solder joint has a desired height and/or shape.
[0025] In an embodiment, the desired shape of the solder joint
comprises an hourglass shape.
[0026] Various embodiments provide a method of forming a solder
joint between a semiconductor chip and a substrate, the method
comprising the steps of: melting a solder disposed between the chip
and the substrate; and solidifying the solder by directing a
cooling stream towards the solder.
[0027] In an embodiment, the cooling stream is directed towards the
solder while a chip and/or substrate heater continue to provide
heat to the chip and/or substrate.
[0028] Various embodiments provide a system for placing a
semiconductor chip onto a substrate comprising: a base; a substrate
holder moveable relative to the base in an x-y plane parallel to
the base; and a bond head moveable substantially only along a fixed
vertical axis relative to the base such that x and y positions of
the bond head relative to the base are substantially fixed.
[0029] In an embodiment, the bond head is mounted to a top plate
moveable substantially only along a fixed vertical axis relative to
the base.
[0030] In an embodiment, the top plate is coupled to two or more
vertical shafts mounted to the base.
[0031] In an embodiment, the bond head comprises pick-up tip
rotatable in a plane parallel to the base.
[0032] In an embodiment, the system further comprises means for
providing the semiconductor chip to the bond head for pick-up,
wherein the means for providing the semiconductor chip is
configured for moving in and out of the fixed x and y positions of
the bond head.
[0033] In an embodiment, the means for providing the semiconductor
chip to the bond head for pick-up is configured in use to heat up
the semiconductor chip before providing the semiconductor chip to
the bond head for pick-up.
[0034] In an embodiment, the system further comprises means for
inspecting alignment of the semiconductor chip on the bond head and
a substrate on the substrate holder, wherein the means for
inspecting the alignment is configured for moving in and out of the
fixed x and y positions of the bond head.
[0035] In an embodiment, the system further comprises means for
cooling the semiconductor chip on the bond head.
[0036] In an embodiment, the means for cooling comprises means for
blowing an airjet onto a portion of the bond head.
[0037] Various embodiments provide a method of placing a
semiconductor chip onto a substrate comprising the steps of:
heating the semiconductor chip, the semiconductor chip having
solder thereon and being heated to a temperature which is higher
than the solder melting point to form molten solder; heating the
substrate to a temperature which is lower than the solder melting
point; and placing the semiconductor chip onto the substrate so
that the molten solder forms a solder joint therebetween to join
the semiconductor chip to the substrate and cause the semiconductor
chip and the substrate to reach an equilibrium temperature which is
higher than the solder melting point.
[0038] In an embodiment, the method further comprises preheating
the semiconductor chip to a temperature which is lower than the
solder melting point before heating the semiconductor chip to the
temperature which is higher than the solder melting point.
[0039] In an embodiment, the method further comprises cooling the
solder joint to below the solder melting point to solidify the
solder.
[0040] In an embodiment, the method further comprises waiting a
predetermined period of time in between the step of placing and the
step of cooling.
[0041] In an embodiment, the method further comprises holding the
substrate in position using a vacuum before the step of
placing.
[0042] In an embodiment, the method further comprises pulling apart
the semiconductor chip and the substrate after the step of placing
to form the solder joint into a predetermined shape.
[0043] In an embodiment, the predetermined shape is an hour-glass
shape.
[0044] Various embodiments provide a system for fluxing
semiconductor chips for bonding comprising: a rotary flux plate
having pockets; means for dispensing a flux material into the
pockets; means for leveling the flux material in the pockets;
wherein the system is configured for indexing the pockets in a
direction from the means for dispensing to the means for leveling
the flux material.
[0045] In an embodiment, the means for dispensing the flux material
comprises a dispensing conduit mounted to an axial support for the
rotary flux plate, wherein a radial position of an outlet of the
dispensing conduit is aligned with a radial position of the
pockets.
[0046] In an embodiment, the means for leveling the flux material
comprises a wiper element mounted to the axial support for the
rotary flux plate, wherein a radial position of a wiping edge of
the wiper element is aligned with the radial position of the
pockets.
[0047] In an embodiment, the wiping edge is level with a surface of
the rotary flux plate.
[0048] In an embodiment, the wiper element is mounted to the axial
support via the dispensing conduit.
[0049] Various embodiments provide a system of selectively fluxing
a substrate comprising of: a flux plate having patterned recesses;
means for dispensing a flux material into the recesses; means for
leveling the flux material in the recesses; and a stamp pad for
transferring the flux material in the recesses onto the substrate
to apply the flux material to selective locations on a surface of
the substrate.
[0050] In an embodiment, the stamp pad is configured in use to
align along its longitudinal axis with the recesses to pick-up the
flux material from the flux plate.
[0051] In an embodiment, the means for dispensing the flux material
into the recesses comprises a flux material reservoir, and wherein
the flux plate is configured in use to move underneath the flux
material reservoir to receive the flux material into the
recesses.
[0052] In an embodiment, the means for leveling the flux material
in the recesses comprises a wiper element disposed on the flux
material reservoir, and wherein the flux plate is configured in use
to move from underneath the flux material reservoir to cause the
wiper element to level the flux material in the recesses.
[0053] In an embodiment, the system further comprises a camera
configured in use to enable inspection of the flux material pattern
transferred to the stamp pad.
[0054] Various embodiments provide a method of selectively fluxing
a substrate, the method comprising the steps of: providing a flux
plate having a pattern of flux material provided thereon; picking
up the flux material using a stamp pad element such that the
pattern of the flux material is transferred to the stamp pad
element; and transferring the patterned flux material from the
stamp pad element to the substrate.
[0055] In an embodiment, the flux plate comprises recesses for
holding the pattern of flux material.
[0056] In an embodiment, the recesses are aligned with a
longitudinal axis of the stamp pad during pick-up of the flux
material.
[0057] In an embodiment, the method further comprises positioning
the flux plate underneath a flux material reservoir, and providing
the flux material into the recesses.
[0058] In an embodiment, the method further comprises removing the
flux plate from underneath the flux material reservoir and leveling
the flux material in the recesses.
[0059] In an embodiment, a wiper element disposed on the flux
material reservoir is used to level the flux material in the
recesses during removal of the flux plate from underneath the flux
material reservoir.
[0060] In an embodiment, the method further comprises inspecting
the flux material pattern transferred to the stamp pad element
using a camera.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] Embodiments of the invention will be better understood and
readily apparent to one of ordinary skill in the art from the
following written description, by way of example only, and in
conjunction with the drawings, in which:
[0062] FIG. 1 shows an overview perspective schematic diagram of a
system for high speed precision assembly of semiconductor packages
according to an example embodiment.
[0063] FIG. 2 shows the different perspective view schematic
diagram of the system layout of the system of FIG. 1.
[0064] FIG. 3 shows a different perspective view schematic diagram
of the system layout of the system of FIG. 1.
[0065] FIGS. 4a), 4b) and 4c) shows the schematic diagram of an
Offset Flipper according to an example embodiment.
[0066] FIG. 5 shows the schematic diagram of a Precision Bond
Module according to an example embodiment.
[0067] FIG. 6 shows the schematic diagram of a Preheater according
to an example embodiment.
[0068] FIG. 7 shows the schematic diagram of a Substrate XY Table
according to an example embodiment.
[0069] FIG. 8 shows the schematic diagram of a Substrate Height
Probe according to an example embodiment.
[0070] FIG. 9 shows the schematic diagram of an Alignment Camera
according to an example embodiment.
[0071] FIG. 10 shows the schematic diagram of a Bond Head according
to an example embodiment.
[0072] FIGS. 11 a) and 11 b) shows the schematic diagram of a
Dieset Structure according to an example embodiment.
[0073] FIGS. 12a), 12b), 12c), and 12d) and enlargement 502
illustrate the operations of a Precision Bond Module process
according to an embodiment.
[0074] FIG. 13 illustrates the temperature profile of semiconductor
chip and substrate during the Precision Bond Module operations of
FIG. 12.
[0075] FIGS. 14a) to c) show schematic drawings illustrating
methods of forming a solder joint between a semiconductor chip and
a substrate according to example embodiments.
[0076] FIG. 15 shows the schematic diagram of a Selective Fluxing
Unit according to an example embodiment.
[0077] FIGS. 16a), 16b), 16c) and 16d) illustrate the sequence of
steps during the selective fluxing operation in one example
embodiment.
[0078] FIG. 17 shows the schematic diagram of a Rotary Flux Plate
according to an example embodiment.
DETAILED DESCRIPTION
[0079] The present invention may be understood more readily by
reference to the following detailed description of certain
embodiments of the invention. While the following description of
the semiconductor package assembly system will use specific
drawings for illustrating the principles of the present invention,
it is apparent that the principles of the present invention are not
limited by these specifics.
[0080] The present invention provides an apparatus that is capable
of processing semiconductor chips in a precise way with high
throughput, where the processes include mechanical motion of
flipping, picking and placing of semiconductor chips onto
substrate. In an embodiment, the semiconductor chip is a flip chip.
FIGS. 1 to 3 show schematic diagrams of different perspective views
of an apparatus 100 for high speed precision assembly of
semiconductor packages according to an example embodiment. Several
functions of the apparatus are performed by several modules
including an Offset Flipper Module 202, a Precision Bond Module 206
and a Selective Fluxing Module 302. Depending on the application
configuration, chip pre-heating in the Precision Bond Module 206 is
used in conjunction with the Selective Fluxing Module 302 as will
be described in more detail below.
[0081] FIGS. 4a), b) and c) show an exemplary embodiment of the
apparatus, the Offset Flipper Module 400, which picks up
semiconductor chip from diced wafer to be transferred to a Transfer
Head 402, for measuring of the semiconductor chip dimensions and
transferring to a Preheater 403 to be placed on a substrate in a
later process. The Offset Flipper Module 400 also includes a chip
height probe 405 for measuring a vertical position (i.e. height) of
the semiconductor chip. It can be seen as shown in FIG. 4a), from a
diced wafer 404, which is mounted on tape (not shown), individual
semiconductor chips are ejected with a die ejector (not shown) from
below upwards, to push/eject the chip out of the tape (not shown),
while the tape (not shown) is being held down by vacuum or
mechanical means. Pick Up Head 406 then picks a chip from the diced
wafer by a synchronized motion between the Pick Up Head 406A and
the die ejector (not shown). The Pick Up Heads 406A, B can be any
known means in the art such as vacuum sucker that picks up the chip
with air pressure and subsequently transfers the chip by releasing
the pressure. To efficiently eject and pick up a chip, the chip has
to be at a predetermined position aligned to the centre of the die
ejector (not shown). The positioning of this chip is achieved with
a vision alignment system (not shown) looking at the chip.
[0082] The Pick Up Heads 406A, B are mounted on a Pick and Flip Arm
408. The Pick and Flip Arm 408 is arranged in such a way that it
rotates in an executed rotation as indicated by arrow 410 about a
pivot point 412, thus flipping the picked up chip by 180 deg. The
Pick and Flip Arm 408 has two opposite Pick Up Heads 406A and 406B,
which allows simultaneous picking up and depositing of two
semiconductor chips, which have been ejected from the diced wafer.
The first Pick Up Head 406A picks up a chip, while the second Pick
Up Head 406B deposits previously picked up chip, which is now
flipped, onto the Transfer Head 402. In this position, the Pick and
Flip Arm 408 is angled to the vertical axis and the Pick Up Head
406A, B does not lie on the same vertical axis.
[0083] As shown in FIG. 4b), the Offset Flipper Module 400 is able
to perform vision check for chips prior to pick up when the Pick
and Flip Arm 408 swings to a vertical position from the pick and
deposit position (compare FIG. 4a) to clear the view for the camera
414 in the vision system (not shown). The vision system
locates/inspects for proper die location so as to provide
information to the chip alignment system (not shown) to perform
chip alignment to the die ejector (not shown), prior to pick up by
the Pick Up Head 406. Besides the Pick and Flip Arm 408 rotating
about the pivot point 412, the Pick Up Heads 406A also travel in
the plane of the drawings as caused by a cam 416. This results in
control of the Z motion of the Pick and Flip Arm 408 with the Pick
Up Heads 406A, B at the bottom of the Offset Flipper Module 400 to
prevent contact with the diced wafer 404 during rotation.
[0084] FIG. 4c) shows further operation of the Offset Flipper
Module 400, wherein the Pick and Flip Arm 408 has rotated to an
opposite position to that of FIG. 4a). Stated differently, in FIG.
4c), the Pick and Flip Arm 408 has swung 180 degrees from the
position shown in FIG. 4a).
[0085] A chip will be transferred from the Pick Up Heads 406A, B to
the Transfer Head 402 with the positioning of the Pick and Flip Arm
408 as shown in FIG. 4a), which will then transfer the chip to be
processed in the Precision Bond Module 206 (FIGS. 1-3).
[0086] The example embodiment described above advantageously
provides a system for pick and transfer of semiconductor chips in
the form of the Offset Flipper Module 400, comprising the rotating
Pick and Flip Arm 408, two pick up heads 406A, B attached at
respective end portions of the Pick and flip Arm 408, and a camera
system including camera 414 for inspecting a chip pick-up position
in a vertical line of sight configuration, wherein an axis of
rotation of the Pick and Flip Arm 408 is offset from the line of
sight. The pick up heads 406A, B are angled relative to a
longitudinal axis of the Pick and flip Arm 408, and are moveably
attached thereto.
[0087] The Offset Flipper Module 400 further comprises means for
retracting the pick up heads during rotation of the pick up heads
406A, B away from the die-pick-up position, in the form of a cam
416 for guiding the pick up heads 406A, B during rotation of the
Pick and Flip Arm 408, in this example embodiment. The camera
system comprises the substantially horizontal camera 414 and a
reflecting element in the form of a mirror 418 for achieving the
vertical line of sight configuration
[0088] The example embodiment can provide a method for pick and
transfer of semiconductor chips. In an embodiment, the
semiconductor chip is a flip chip. In an embodiment, the method
comprises the steps of providing a rotating arm, providing two pick
up heads attached at respective end portions of the rotating arm,
providing a camera system for inspecting a die pick-up position in
a vertical line of sight configuration; and rotating the rotating
arm for pick and transfer of the semiconductor chips, wherein an
axis of rotation of the rotating arm is offset from the line of
sight.
[0089] FIG. 5 illustrates the Precision Bond Module 206 in an
exemplary application configuration for bonding the semiconductor
chips comprising interconnections such as copper pillar bumps to a
substrate. The Precision Bond Module 206 as shown in FIG. 5
consists of the Bond Head 504 with airjet cooling channel (not
visible in this view), the Substrate XY Table 506, the Alignment
Camera 508, the Die-set Structure 1100, a Substrate Height Probe
1200, and a Rotary Preheater 1502.
[0090] FIG. 6 shows the Rotary Preheater 502. This Rotary Preheater
502 receives the chip from the Transfer Head 402 and performs a
preheating process in which the chip undergoes gradual heating from
room temperature to a first temperature preferably below the
melting point of a solder, so as to preferably assist in preventing
thermal shock on the chip. The Rotary Preheater 502 includes an
indexing mechanism (not shown) to drive the Turret 705 carrying the
chips, Heater Block 704 and a means to maintain a gap between the
Heater Block 704 and the Turret 705. The chip is placed on and
indexed around the Turret 705, and heated by radiation and
convection from the Heating Block 704, which incorporates several
Heater Elements 707 disposed above indexing locations of the chips
on a Turret 705. Details of the Rotary Preheater 502 for use in
example embodiments have been described in published PCT
application no. PCT/SG2007/000441, the contents of which are hereby
incorporated by cross-reference. The pre-heated chip will then be
picked up by the Bond Head 504.
[0091] FIG. 7 shows the Substrate XY Table 506. This Substrate
Table 506 comprises of a vacuum chuck/clamps with built in heating
components (not shown) and a motorised XY stage 902. The operating
procedure in one embodiment can be as follows; to hold down the
substrate 904 firmly by means of vacuum/clamps (not shown) during
the entire bonding process, to heat up the substrate 904 to a
second temperature, to enable the substrate 904 on the XY stage 902
to be moved to various bonding locations and for making fine
movements for offset correction during alignment.
[0092] FIG. 8 shows a Substrate Height Probe 1200. The Substrate
Height Probe 1200 allows the height of the substrate to be measured
after it has been firmly held by the Substrate XY Table 506 (FIG.
5). The Substrate Height Probe 1200 comprises a probe element 1202,
a guidance system 1204 for vertical displacement of the probe
element 1202, and a precision measurement scale and encoder 1206
coupled to the guidance system 1204.
[0093] FIG. 9 shows the Alignment Camera 508. The Alignment Camera
508 uses collinear vision alignment cameras 1002, 1004 to capture
and process the images of fiducial points on the chip and substrate
concurrently and provision of the data to controller (not shown)
via cables 1005, 1007 to calculate the relative offset in XY
coordinates and the theta offset. The Alignment Camera 508
comprises the pair of cameras 1002 and 1004, one each for chip and
substrate, top and bottom ring light 1006, which would be effective
for images of chips/substrates with protruded features e.g. bumps,
coaxial light 1008, 1009, which would be effective for images of
chips/substrates with flat reflective surfaces e.g. wafer surface.
Optical elements (not shown) are disposed in the housing 1010 to
create the optical paths from the cameras 1002 and 1004 to
respective co-axial lenses e.g. 1012. The Alignment Camera 508 can
be driven in the XYZ axis by a motor (not shown).
[0094] The Bond Head 504 is shown in FIG. 10, and allows the chip
to be heated to a third temperature preferably above the melting
point of the solder on the bumps, such that there is sufficient
thermal energy for a solder joint. The Bond Head 504 can be mounted
on the Dieset 510 (FIG. 5) and coupled with a motor for die
rotation during an alignment process prior to bonding. Upon contact
between the pre-heated die and the pre-heated substrate, the
junction temperature of the chip and the substrate reaches an
equilibrium fourth temperature, which is preferably higher than the
melting point of the solder. Following a bonding period, the Bond
Head 504 enables solidification of the molten solder by momentarily
cooling down the otherwise hot Bond Tool 803 by a concentrated and
guided stream of compressed air onto the tip 802 of the Bond Tool
803. As will be appreciated, this can preferably facilitate faster
cooling of the junction temperature to below the solder melting
point. Also, this can preferably allow the bond heater 805 to
remain heated, thus maintaining the Bond Head 504 at a
substantially constant temperature between pick-up and bonding of
chips, which can in turn result in faster processing time and/or
more stable operation conditions. The Bond Tool 803 is preferably
made of a material with high thermal conductivity and low specific
heat capacity properties. A cooling channel 806 to carry and focus
the jet of air to the tip 802 of the Bond Tool 803 is separated
from the body of the Bond Head 504 by an insulating plate 808.
[0095] The example embodiment described above advantageously
provides a device for bonding a semiconductor chip onto a substrate
in the form of Bond Head 504 comprising the pick-up tip 802 for the
chip, the heater 805 for heating the pick-up tip 802 for heating of
the chip prior to bonding, and means for directing a gaseous
cooling stream towards the pick-up tip 802, here in the form of the
airjet cooling channel 806 mounted to a main mounting block 810 of
the Bond head 504. The pick-up tip 802 is attached on the mounting
block 810, and the heater 805 is disposed in the mounting block
810. The cooling channel 806 is mounted to the mounting block 810
via the thermally insulating plate 808. In this embodiment, the
cooling channel 806 is configured to direct the cooling stream from
three sides of the mounting block 810 towards the pick-up tip 802.
The cooling channel 806 is configured to receive the cooling air
stream in a downward direction along one side of the mounting block
810, and has a diverting portion, here in the form a ledge 812
extending inwardly towards the pick-up tip 802, for diverting the
cooling stream substantially horizontally towards the pick-up tip
802 mounted at the bottom of the mounting block 810.
[0096] FIG. 11a) and b) shows a Dieset Structure 1100 according to
an example embodiment. The Dieset Structure 1100 provides a
structure to deliver high degree and long lasting parallelism
between the Bond Head 504 (FIG. 5) and the XY Table 506 (FIG. 5).
The Dieset Structure 1100 consists of a Dieset top plate 1102, with
an interference fit in a ball-shaft assembly (e.g. 1104, 1106 to a
bottom Dieset plate 1108.) This assembly preferably allows maximum
rigidity and minimum radial shift during vertical motion. A
motorized actuator (not shown) enables the relative motion between
the Dieset plates 1102, 1108. The presence of a measurement system
(not shown) allows precise measurement of displacement between the
two plates 1102, 1108 of the Dieset Structure 1100. In this
embodiment, the Dieset plates 1102, 1108 are coupled via fours
shafts 1110 to 1113 for allowing maximum rigidity and minimum
radial shift during the vertical motion.
[0097] FIG. 12a) to e) illustrate the sequence of activities that
take place in the Precision Bond Module 206 in one application
configuration. FIG. 13 shows the associated temperature profile
during the sequence of activities. When a chip first arrived at the
Precision Bond Module 206 from the Offset Flipper 400 (FIG. 4), the
chip height is measured (FIG. 12a) using a chip height probe 511,
(measurement location 512) and the chip is dispensed onto a Rotary
Preheater 502 (FIG. 12b). The Rotary Preheater 502 heats up the
chip to a temperature 1 and the pre-heated chip is then handed over
to a Bond Head 504 (FIG. 12c), on which the chip is further heated
to a temperature (temperature 2) higher than the solder melting
point. Also during the step shown in FIG. 12a) a substrate is
dispensed onto a Substrate XY Table 506 and being held down by
strong vacuum. The substrate will be heated to a temperature 3 on
the Substrate XY Table 506. The height of the substrate is measured
post-heating by a Substrate Height Probe (not shown). The Substrate
XY Table 506 then moves to the bonding location.
[0098] As shown in FIG. 12d), an Alignment Camera 508 moves in
between the Substrate XY Table 506 and the Bond Head 504 and
processes fiducial marks on chip and substrate using collinear
vision to determine the relative offset in XY and theta directions
between the die on the Bond Head 504 and the relevant bond location
on the Substrate XY Table 506. The alignment Camera 508 then
retracts (FIG. 12e). The Bond Head 504 mounted on the Dieset 510
makes a theta correction and the XY Table 506 makes the correction
in the X and Y axis. The Dieset 510 makes a calculated vertical
bond stroke downward based on the height calculated by the
controller (not shown). Upon contact, the junction of the chip and
the substrate reaches an equilibrium temperature 4, which is higher
than the melting point of solder. With reference to FIG. 13, which
shows the temperature profiles of the chip and substrate during the
operations described, the chip and the substrate are held at the
temperature 4 for a certain time sufficient for the solder bond to
occur. The Bond Head 504 airjet cooling channel then blows air to
the tip of the bond tool to drop the junction temperature
(temperature 5) of the chip and substrate below the melting point
of solder. The Bond Head 504 then releases the chip and the Dieset
510 retracts the Bond Head 504.
[0099] The example embodiment described above advantageously
provides a system for placing a semiconductor chip onto a substrate
in the form of Dieset 510 comprising a base in the form of a base
plate 514, a substrate holder in the form of XY table 506 moveable
relative to the base plate 514 in an x-y plane parallel to the base
plate 514, and the Bond Head 504 moveable substantially only along
a fixed vertical axis relative to the base plate 514 such that x
and y positions of the Bond Head 504 relative to the base plate 514
are substantially fixed. The Bond Head 504 is mounted to a top
plate 516 moveable substantially only along the fixed vertical axis
relative to the base plate 514. The top plate 516 is coupled to two
or more vertical shafts 518, 520 mounted to the base plate 514. The
Bond Head comprises pick-up tip rotatable in a plane a parallel to
the base plate 514. The Dieset 510 further comprises means for
providing the semiconductor chip to the bond head for pick-up, here
in the form of a Preheater 502 configured for moving in and out of
the fixed x and y positions of the Bond Head 504. The Dieset 510
further comprises means for inspecting alignment of the
semiconductor chip on the bond head and a substrate on the
substrate holder, here in the form of Alignment Camera 508
configured for moving in and out of the fixed x and y positions of
the Bond Head 504. In an embodiment, the semiconductor chip is a
flip chip.
[0100] In one example embodiment, the bond stroke calculation is
based on chip, substrate, reference heights, which are all machine
measured, and compression, which is a value to overcome any
co-planarity variances from the chip and the substrate and also to
obtain the desired standoff between the chip and substrate. In an
embodiment, the chip height is measured using a chip height probe
509. In an embodiment, the substrate height is measured using the
substrate height probe 1200. The reference height is the vertical
distance between the surface of the Substrate XY Table 506 and the
surface of the Bond tool tip 802 (FIG. 10). The bond vertical
stroke is obtained by calculating the difference between the
reference height and the substrate and the die heights, and then
adding the compression value. After reaching the bond stroke, where
the solder in a liquid state makes contact for bonding, a small
pullback stroke can be introduced to displace the chip away from
the substrate to obtain a desired solder shape and a desired
height, for example, an hourglass shape. The bond head airjet
cooling channel then blows air to the tip of the bond tool to drop
the temperature of the chip and substrate below the melting point
of solder to solidify the solder to retain the height/shape
formation. The bond head then releases the chip and retracts fully
away from the substrate.
[0101] In an embodiment, the Bond Head 504 may be maintained at a
constant temperature during the bonding process, and this
temperature may be higher than the melting point of the solder. In
an embodiment, there may be no heating or cooling from the Bond
Head 504. Instead, an instantaneous dip in temperature to solidify
the solder joint may be provided by the airjet stream targeted at
the Bond tool tip 802 which interfaces between the Bond Head 504
and the chip. Accordingly, the bulk of the system does not need to
go through temperature changes.
[0102] In an embodiment, the Preheater 502 provides a gradual rise
in chip temperature to reduce the temperature differential between
the chip and the Bond Head 504. In turn, this may prevent thermal
shock when the Bond Head 504 picks up the chip.
[0103] It will be appreciated that the solder can be melted by
various different methods in different embodiments, including "Melt
and Touch" i.e. the solder on the die is molten prior to contact on
the substrate, upon contact to the substrate the molten solder
reflows onto corresponding pads/bumps on the substrate; "Touch and
Melt", i.e. the die reaches a temperature higher than the melting
point of solder, upon contact to the substrate the heat from the
die melts the solder on the corresponding pads/bumps on the
substrate, or the die is at a temperature lower than the melting
point of solder, upon contact to the substrate, heat is applied to
the die to melt the solder.
[0104] With reference to FIG. 14a) to c), the example embodiments
described above advantageously provide a method of forming a solder
joint between a die 1700 and a substrate 1702, the method
comprising the steps of melting a solder 1704 disposed between the
die 1700 and the substrate 1702, the die 1700 and the substrate
1702 being separated by a distance d1, retracting the die 1700 from
the substrate 1702 while the solder 1704 is in a molten state such
that the die 1700 and the substrate 1702 are separated by a
distance d2, and solidifying the solder 1704 while the die 1700 and
substrate 1702 are separated by distance d2. The solidifying of the
solder 1704 comprises directing a cooling stream towards the solder
1702. The cooling stream is directed towards the solder 1704 while
a die and/or substrate heater (not shown) continue to provide heat
to the die 1700 and/or substrate 1702 in this embodiment. The
distance d2 is chosen such that the formed solder joint 1706 has a
desired height and/or shape. The desired shape may comprise an
hourglass shape.
[0105] Also with reference to FIG. 14a) to c), the example
embodiments described above advantageously provide a method of
forming a solder joint between the die 1700 and the substrate 1704,
the method comprising the steps of melting a solder 1704 disposed
between the die 1700 and the substrate 1702, and solidifying the
solder 1704 by directing a cooling stream towards the solder 1704.
The cooling stream is directed towards the solder 1704 while the
die and/or substrate heater (not shown) continue to provide heat to
the die 1700 and/or substrate 1702, in this embodiment.
[0106] It will be appreciated by a person skilled in the art, that
various solder configuration and techniques may be applied in
different embodiments. For example, solder bumps may be provided on
the die and/or the substrate, and the bonding may involve heating
the die and/or the substrate within the Precision Bond Module 206,
or in a separate re-flow oven.
[0107] FIG. 15 shows the Selective Fluxing Module 302. The
Selective Fluxing Module 302 comprises of a Flux Transfer Arm 1302,
Flux Camera 1304, Substrate Holder 1306, Flux Plate 1308, Artwork
on Flux Plate 1310, Stamp Pad 1312 and Flux Reservoir 1314. This
Selective Fluxing Module 302 operates in the step illustrated in
FIG. 12a) to apply flux on selective locations on the surface of a
substrate 1309. The Artwork 1310 defines the corresponding
selective locations that are to be fluxed on the substrate
1309.
[0108] FIG. 16a) to d) illustrate the sequence of steps during the
selective fluxing operation in one example embodiment. Step 1 (FIG.
16a) shows Stamp Pad 1312 positioned over Artwork 1310 filled with
flux. In step 2 (FIG. 16b) the Stamp Pad 1312 picks up flux from
the Flux Plate 1308 and then aligns to the substrate 1309 in step 3
(FIG. 16c) based on information from the look down substrate camera
1300 (FIG. 15). The Stamp Pad 1312 then transfers the flux onto the
substrate 1309, for example onto solder bumps 1402, in step 4 (FIG.
16d).
[0109] The example embodiment described above advantageously
provides a method of selectively fluxing of a substrate, the method
comprising the steps of providing the flux plate 1308 having a
pattern of flux material, here in the form of artwork 1310 provided
thereon, picking up the flux material using the Stamp Pad 1312 such
that the pattern of the flux material is transferred to the Stamp
Pad 1312, and transferring the patterned flux material from the
Stamp Pad 1312 to the substrate 1309. The artwork 1310 comprises
recesses e.g. 1316 for holding the pattern of flux material. The
recesses 1316 are aligned with a longitudinal axis of the Stamp Pad
1312 during pick-up of the flux material. The method further
comprises positioning the flux plate 1308 underneath the flux
material reservoir 1314, and providing the flux material into the
recesses e.g. 1316. The method further comprises removing the flux
plate 1308 from underneath the flux material reservoir 1314 and
leveling the flux material in the recesses e.g. 1316. A wiper
element, here in the form of a radial wiper 1318 disposed on the
flux material reservoir 1314, is used to level the flux material in
the recesses e.g. 1316 during removal of the flux plate 1308 from
underneath the flux material reservoir 1314. The method further
comprises inspecting the flux material pattern transferred to the
Stamp Pad 1312 using the camera 1300.
[0110] FIG. 17 shows the Rotary Flux Plate 1502 which may replace
the Rotary Preheater in an alternative configuration, the chip Pick
and Place Arm 402 (FIG. 4) provided to pick up the die from the
Pick and Flip Arm 408 (FIG. 4) dispenses the die onto the Rotary
Flux Plate 1502 that indexes at fixed intervals. Chips e.g. 1600
can be dispensed following each index of the Rotary Flux Plate
1502. The Rotary Flux Plate 1502 provides multiple pockets e.g.
1504 having predetermined depths and area for filling with flux
using the dispensing channel 1506 (FIG. 5). The wiper 1508 levels
out the flux in the pockets e.g. 1602. Chips e.g. 1600 being
dispensed into the pockets e.g. 1504 of flux would thus have a
predetermined flux height on the bumps (not shown). The Bond Head
504 picks up the fluxed chip e.g. 1606 for bonding to the substrate
(not shown). It is noted that bonding between the substrate and the
chips may proceed within the Precision Bond Module without
pre-heating of the chip in this alternative configuration.
[0111] The example embodiment described above advantageously
provides a system for fluxing semiconductor chips for bonding,
comprising the rotary flux plate 1502 having pockets e.g. 1504,
means for dispensing a flux material into the pockets e.g. 1504,
here in the form of a dispensing channel 1506, and means for
leveling the flux material in the pockets e.g. 1504, here in the
form of a wiper 1508. The rotary flux plate 1502 is configured for
indexing the pockets e.g. 1504 in a direction from the dispensing
channel 1506 to the wiper 1508. The dispensing channel 1506 is
mounted to an axial support 1510 for the rotary flux plate 1502,
wherein a radial position of an outlet 1512 of the dispensing
channel is aligned with a radial position of the pockets e.g. 1504.
The wiper 1508 is mounted to the axial support 1510 for the rotary
flux plate 1502, wherein a radial position of a wiping edge 1514 of
the wiper 1508 is aligned with the radial position of the pockets
1504. The wiping edge 1514 is level with a surface of the rotary
flux plate 1502, and is mounted to the axial support 1510 via the
dispensing channel 1506 in this embodiment. In an embodiment, the
semiconductor chip is a flip chip.
[0112] Some of the above-described embodiments disclose the use of
dies. It is to be understood that in an embodiment, a die comprises
one or more integrated circuits which are to become a semiconductor
chip. Accordingly, in an embodiment, the terms `die` and
`semiconductor chip` may be interchangeable.
[0113] It will be appreciated by a person skilled in the art that
numerous variations and/or modifications may be made to the present
invention as shown in the specific embodiments without departing
from the spirit or scope of the invention as broadly described. The
present embodiments are, therefore, to be considered in all
respects to be illustrative and not restrictive.
* * * * *